Why it's important to open a credit card at age 18

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Young adults have enough to worry about without giving second thought to their credit scores. Yet that three-digit number can have a big impact on your financial life, and the better your score, the easier it will be to lease your first apartment, buy a car and even embark on a new career, as employers frequently check your score before you're hired.

While understanding personal finance might seem intimidating for the uninitiated, the basics are fairly straightforward. A good place to start is by opening a credit card at 18, so you can start building credit at an early age and developing good money habits.

Below, we review why it's important to get a credit card at 18 and what you can do to protect your credit score as a new cardholder.

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The third most important factor in achieving a good credit score (after making on-time payments and keeping your total debt low) is your length of credit history, or the amount of time you've had credit accounts in your name. Potential lenders like to see that you can keep your credit accounts in good standing for years to come.

In fact, an overwhelming majority (92%) of people who have a perfect 850 credit score are either Gen Xers or Baby Boomers, according to Experian's research. This shows that while it's still possible to have a perfect credit score in your 20s and 30s, consumers with long credit histories have a major advantage. Credit expert Jim Droske, who has a perfect credit score, shared with CNBC Select that the average age of his credit card accounts is 10 years and 11 months and his oldest account is 34 years and 10 months. 

A good credit score offers you many advantages. Most notably, you'll qualify for the best rates on loans and credit cards, and it can also impact your auto and home insurance rates. If you have an excellent credit score, you may qualify for the best rewards credit cards. Perhaps most surprisingly, having a good credit history increases the chance you'll get that job or promotion if your employer requests a review of your credit report.

Another reason it's crucial to open a credit card is to avoid being credit invisible. When you're credit invisible, you have no record to prove your ability to borrow money.

For instance, let's say that you decide you want to finance your first car, take out a mortgage on a home or open a small business. Unless you have a massive reserve of cash, you'll need to apply for a loan, and it's a lot more difficult if you have no credit history.

If you were to save up the cash needed to cover these kinds of expenses, you'd have to save for years in order to afford it. Having access to affordable loans helps you finance some of life's necessities in ways that fit your budget and offer more opportunities to enjoy the life you want.

You can be an authorized user as young as 13, but you have to be 18 to sign up for your first credit card on your own.

When you're ready for this step, you'll need to be prepared to show some documentation. Due to the CARD Act of 2009, applicants between ages 18 and 21 must show proof of verifiable income, such as a pay stub, tax returns, commission checks or investment statements. This measure is to prevent lenders from approving young applicants for high-limit credit cards they're not well-equipped to pay back.

While you can sign up for your first credit card at 18, it's best to wait until you have confidence in your ability to pay off your balances on time and in full, while balancing other financial obligations like rent, utilities, tuition, transportation and groceries. Fortunately, the best cards for building credit come with helpful incentives that encourage good habits from the beginning. 

For example, Capital One Platinum Secured Credit Card cardholders are automatically considered for a higher credit limit after making six months of regular, consecutive on-time payments; As it is a secured card, you'll need to make a refundable qualifying deposit starting as low as $49, $99 or $200 (based on your creditworthiness) to access an initial credit limit.

Likewise, Capital One's other credit-building credit cards encourage the same best practices. The Capital One QuicksilverOne Cash Rewards Credit Card and the Capital One Platinum Credit Card come with a minimum credit limit that can grow over time as you fulfill your borrower agreements and build a record of dependability.

The Discover it® Student Cash Back is also meant for credit card newcomers, and it encourages responsible credit behavior with cash-back rewards. It offers 5% cash back on the first $1,500 in purchases in rotating categories each quarter (when you activate), then 1% cash back. Plus, for new cardmembers Discover will match the cash back you earn in the first year of card membership.

But even without such incentives, there are a few easy tips to follow to help you stay out of debt and make the most of having a credit card.

First and foremost, remember that simply having an account doesn't instantly help your credit score. "Credit scores require that there be activity on that account," Rod Griffin, senior director of public education and advocacy for Experian, tells CNBC Select.

The easiest way to do this?  "Use your account to make a small purchase every month then turn around and make the payment every month," Griffin advises.

And if you plan to use your credit card for everyday spending, try to charge no more than 10% to 30% of your credit limit on your card at once. So if you start with a limit of $500 on your first credit card, limit your charges to no more than $150 each month. Doing this helps you keep your debt-to-credit ratio low (the second-most factor in your credit score), but most importantly it gets you in the habit of only spending what you can afford to pay off each month.

Most importantly, pay your bills on time; this is the biggest factor in your score. Lenders are more willing to give you credit when they see a long history of on-time payments on your credit report, even if you have some debt in your name. However, when possible, always pay your bills in full so that you never have to pay over-the-limit fees or interest on the balance.

By following these simple rules of thumb, you'll start your young adult life on firm footing with good credit to your name.

There's a frustrating catch-22 you face when you're ready to establish credit: Lenders are less likely to see you as a reliable borrower unless you have a good credit history, but it's hard to develop any track record without having credit to begin with.

But while you can't speed up time and jump-start your average credit age, you can set yourself up for success by applying for a good starter credit card at age 18. This will probably be either a secured credit card, a college student credit card (if you're in college) or a credit-building credit card.

After a few years of using your card responsibly, your score will reflect this positive credit history. And if you maintain those good habits, you should be able to take advantage of a good credit score for years to come.

At CNBC Select, our mission is to provide our readers with high-quality service journalism and comprehensive consumer advice so they can make informed decisions with their money. Every personal finance article is based on rigorous reporting by our team of expert writers and editors with extensive knowledge of personal finance products. While CNBC Select earns a commission from affiliate partners on many offers and links, we create all our content without input from our commercial team or any outside third parties, and we pride ourselves on our journalistic standards and ethics.

For rates and fees of the Discover it® Student Cash Back, click here.